这里使用相册Album和图片Picture的关系做示例
1，Album与Picture最基本的关系是1-n(一个相册可以有多张图片)
这时Album、Picture实体类可以这么定义
/// <summary>
/// 相册
/// </summary>
public class Album
{
public int ID { get; set; }
/// <summary>
/// 标题
/// </summary>
public string Title { get; set; }
public DateTime CreateTime { get; set; }
/// <summary>
/// 拥有者
/// </summary>
public virtual User Owner { get; set; }
}
/// <summary>
/// 图片
/// </summary>
public class Picture
{
public long ID { get; set; } public string Title { get; set; } public string Uri { get; set; } public DateTime CreateTime { get; set; } /// <summary>
/// 所属相册
/// </summary>
public virtual Album Album { get; set; }
}
生成的表结构
2，后来就要改需求了，相册要加一个封面
于是Album与Picture的关系就加了一个1-1（一个相册只有一个封面）
这样就需要配置一下实体关系来区分属性之间的关系
Album和Picture类做一些修改
/// <summary>
/// 相册
/// </summary>
public class Album
{
public int ID { get; set; }
/// <summary>
/// 标题
/// </summary>
public string Title { get; set; }
public DateTime CreateTime { get; set; }
/// <summary>
/// 拥有者
/// </summary>
public virtual User Owner { get; set; }
/// <summary>
/// 封面
/// </summary>
public virtual Picture Cover { get; set; }
/// <summary>
/// 相册下的图片列表
/// </summary>
public virtual ICollection<Picture> Pictures { get; set; }
}
/// <summary>
/// 图片
/// </summary>
public class Picture
{
public long ID { get; set; } public string Title { get; set; } public string Uri { get; set; } public DateTime CreateTime { get; set; } /// <summary>
/// 所属相册
/// </summary>
public virtual Album Album { get; set; }
}
然后添加一个映射类
public class AlbumMap:EntityTypeConfiguration<Album>
{
public AlbumMap() {
this.HasMany<Picture>(a => a.Pictures).WithRequired(p=>p.Album);
}
}
EF上下文类中重写方法
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();//移除复数表名的契约
modelBuilder.Configurations.Add(new AlbumMap());
}
数据库迁移时生成的代码：
public partial class AlbumAddCover : DbMigration
{
public override void Up()
{
DropForeignKey("dbo.Picture", "Album_ID", "dbo.Album");
DropIndex("dbo.Picture", new[] { "Album_ID" });
AddColumn("dbo.Album", "Cover_ID", c => c.Long());
AlterColumn("dbo.Picture", "Album_ID", c => c.Int(nullable: false));
CreateIndex("dbo.Album", "Cover_ID");
CreateIndex("dbo.Picture", "Album_ID");
AddForeignKey("dbo.Album", "Cover_ID", "dbo.Picture", "ID");
AddForeignKey("dbo.Picture", "Album_ID", "dbo.Album", "ID", cascadeDelete: true);
} public override void Down()
{
DropForeignKey("dbo.Picture", "Album_ID", "dbo.Album");
DropForeignKey("dbo.Album", "Cover_ID", "dbo.Picture");
DropIndex("dbo.Picture", new[] { "Album_ID" });
DropIndex("dbo.Album", new[] { "Cover_ID" });
AlterColumn("dbo.Picture", "Album_ID", c => c.Int());
DropColumn("dbo.Album", "Cover_ID");
CreateIndex("dbo.Picture", "Album_ID");
AddForeignKey("dbo.Picture", "Album_ID", "dbo.Album", "ID");
}
}
最终表结构
上一节：【EF Code First】 一对多、多对多的多重关系配置
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